Field of the Invention
This invention relates to a method of magnetizing high energy rare earth alloy magnets, and more particularly to a method of imparting to a magnetic alloy basic sophisticated pattern of north and south poles.
High energy rare earth alloy magnetic materials requires a high magnetizing field strength to charge the materials to saturation. A long established "rule of thumb" is that the field strength required for saturation is five to six times the value of the intrinsic coercive force (Hci). Thus, with high energy, modern day magnetic materials, charging fields of 40 to 100 kiloOersteds would not be uncommon to insure saturation. From both a technical and economical view point, this is a great concern to magnet manufacturers and magnet users. Many times, the users will purchase magnetic materials from the alloy manufacturers and either machine or have the alloy blanks machined into the desired shape to suit the ultimate purpose. To facilitate handling during shipping and machining, the magnetic alloy material should be in the demagnetized state during these times. In fact, it is most desirable that the magnetic alloy be magnetized after assembly into the device in which it is employed. For example, in the manufacture of a D.C. brushless motor, the magnetic component having the predesigned shape to precisely fit in the motor is first assembled and then magnetized. This is not always practical because of the configuration of the device, which either prevents the proximate location of the magnetization coil or other magnetization device or serves as a flux shunt thereby directing the charging field away from the magnet.
Further, the user who generally charges the magnet material, does not always possess the equipment capable of developing sufficient high fields to saturate these high energy magnets. For example, a mild steel core electromagnet will generate a maximum field of about 24 kOe. Therefore, should a larger field be required to charge a high energy rare earth alloy magnetic material, a different device must be employed.
Where very high fields are necessary, to charge high energy magnets, impulse magnetizers are employed. While these devices develop instantaneous fields sufficiently large to substantially fully saturate all known permanent magnet materials, they may not be technically feasible for use where a magnet is required to have tiny multiple poles (such as an application for a small stepping motor) or complex pole patterns. This is due to the practical limitation to the amount of required current that can be passed through the small electromagnetic coils employed in the charging process without damaging the coils.
Therefore, there is a definite need to provide a way to saturate high energy rare earth magnetic materials at the lowest possible field strength. Also, there is a need to magnetize high energy rare earth magnetic materials in a discrete pattern of north and south poles.